This invention relates generally to pressure sensitive switches and more particularly concerns switches for the detection of the presence or absence of a person from a hospital bed, wheelchair, baby carriage or any other body supporting structure with respect to which it may be useful to determine the status of occupancy, and to the method of making such switches.
Pressure sensitive switches presently used in many hospital facilities are disclosed in previously issued U.S. Pat. Nos. 4,484,043 and 4,565,910. In these known devices, broad bands of conductive material are used in upper and lower layers such that contact of any portion of the broad upper band with any portion of the broad lower band will complete a circuit between input and output conductors connected to the bands.
While these switches work quite effectively, they are somewhat difficult of manufacture in a manner providing consistency and predictability of operation and consequently are sufficiently expensive to limit their broad use as single use disposable devices. Furthermore, while they work quite well in sensing the presence or absence of fully grown adults, as lesser weights are applied to the switch, sensing reliability somewhat diminishes. The problem of providing a switch having reliable characteristics over a broad weight range is complicated by the requirement that the switch must not only reliably close upon the application of a minimal threshold weight, but must also reliably return to its open condition upon the removal of that threshold weight. In present devices, weights resulting in at least 50 to 75 psi are necessary to achieve desired levels of reliability. In addition, known devices are of relatively thick profile and stiffness so as to provide adequate separation of the conductive bands. This results in a diminishing of patient or occupant comfort and also in a diminishing of the impact of pressure on its operation, contact more frequently being achieved by a crimping or kinking of the device than by flex due to pressure. And known devices are not completely sealed and, therefore, do not provide a fluid or water impervious device, thus compromising the device's integrity and consistency of operation. It is therefore an object of this invention to provide a pressure sensitive switch which will reliably close at relatively low threshold pressures. It is also an object of this invention to provide a pressure sensitive switch which will reliably open on release of the threshold pressure from the switch. It is further an object of this invention to provide a pressure sensitive switch having gridded conductive surfaces with a limited matrix of contact points so as to minimize the possibility of circuit completion in the absence of a relatively low threshold pressure. It is similarly an object of this invention to provide a pressure sensitive switch having gridded conductive surfaces with a limited matrix of contact points separated by a gridded dielectric to minimize the possibility of circuit completion upon release of the threshold pressure. Another object of the invention is to provide a pressure sensitive switch that lends itself to ease in mass production with minimal impact on predictability and consistency in switch operation. A further object of this invention is to provide a pressure sensitive switch of relatively thin and flexible profile so as to maximize patient comfort and to minimize the possibility of crimping or kinking and resultant inadvertent contact. And it is an object of this invention to provide a pressure sensitive switch which is impervious to water and other fluids.